The present invention relates to a reclosable mast comprised in a drilling rig for excavating extraction wells, e.g. oil wells.
Said rig is suitable for use on the ground and can be transported from one location to another by means of trucks and semitrailers.
Said rig normally comprises a mast, a substructure, a hoist and a structure for supporting the vertical or setback drill pipes.
Said substructure is made up of base elements resting on the ground, which is leveled and compacted prior to installing the rig; a central structure at the centre of the well, essentially consisting of two strong shoulders; a latticed structure consisting of two side shoulders and a back, with the fourth side left open. Said latticed structure comprises beams for supporting the rotary table, and the structure for supporting the vertical or setback drill pipes. In addition, said latticed structure is hinged to the base elements and can rotate by 90°, e.g. from horizontal to vertical, and vice versa.
At the top of said latticed structure there are a plurality of connectors, e.g. double-hinged ones, for securing the mast.
There are also connection elements for lifting means used for erecting the assembled mast, once the assembly is completed, e.g. two hydraulic cylinders.
The structure that supports the vertical drill pipes and the beams that support the rotary table are hinged to the substructure, normally at the front leg of the lattice. Said setback and rotary table beams remain substantially horizontal, and take their final configuration when the mast is in the vertical position.
The hoist frame is an articulated parallelogram.
In the final installed position, the hoist frame is secured to the floor where drilling will take place.
The mast has a three-sided latticed structure, in particular with two side shoulders and a back, the fourth side being open. Normally these masts can be divided into a plurality of portions, e.g. four, such as an upper portion, also comprising portions of the hoist, the upper intermediate portion, the lower intermediate portion and the lower portion.
The ground is drilled by means of specific drilling equipment, called “top drive”, comprising at least one drill head slideable on guides which are normally installed on the back of the mast lattice.
The upward/downward motion of said top drive and of the drill string constrained thereto is ensured by a handling system comprising a winding drum, a line, a plurality of pulleys, whereon said line is suitably arranged, and a backup line spooler.
Since the line is subject to wear against the pulleys, it is common practice to pull the line from the spooler and cut it at regular intervals, expressed in tonkm or tonmiles.
Normally the mast in the extended configuration has a nominal distance between its shoulders of 9.144 m and a maximum dimension of 9.16 m. These characteristics ensure sufficient room on the drill floor and very good visibility of the top drive.
The on-site installation of the drilling rig is completed by adding gangways and ladders, a BOP system, and the drill pipe loader.
The above-mentioned drilling rig is normally used for excavating wells which are relatively not very deep, and which require an average installation time of approximately one month. As a consequence, at regular intervals of about one month it is necessary to disassemble said rig, transport it, and reposition it where a new wellbore is to be drilled.
When transporting the rig, in particular in highly urbanized areas, e.g. near towns, it is necessary to solve a problem related to the width of the mast structure, so as to be allowed to drive on two-way two-lane state highways and county roads.
In such cases, an exceptional transportation needs to be arranged, wherein the route must be approved and authorized by the road authorities.
To reduce the cost and time necessary for obtaining the required authorizations, it is necessary that the maximum transversal width of the mast is 3.3 m, so that it can be transported with the aid of a technical escort alone including a car and authorized personnel, without requiring the intervention of the highway police.
Masts are known which can be dismounted and reclosed in order to reduce their dimensions.
Said masts can be disassembled into a plurality of sections. Said mast is divided into sections prior to transportation, and the lateral dimension of the back thereof is reduced in every single section.
In order to take less room, said masts must be divided into sections before they can be reclosed.
U.S. Pat. No. 6,594,960 describes a mast which can be divided into four portions, and which is then reclosed by releasing rear bars forming the back of the mast; the rear bars can be folded through manual means only after the mast has been divided into four portions.
When closing the back of the mast, the rear bars fold up and occupy a portion of the mast structure that, when in use, is occupied by the drilling equipment or top drive. In said mast, the top drive must be removed before one can carry out the mast closing operation.
United States patent application US2011120043 is also known, which describes a sectionable mast whose sections can be brought into a closed configuration.
In both of these prior-art solutions, assembling and disassembling said masts, e.g. in view of transporting them to other drilling locations, require excessive time because of the complexity of the structure and the large number of constrained members that must be fastened or released for properly assembling/disassembling the mast; in fact, in order to properly assemble/disassemble the mast it is necessary to constrain/release a large number of fastening elements included in each mast section.
As a matter of fact, the various sections of the mast must be assembled after having been extended, thus taking up more space and making the parts more difficult to connect.
Furthermore, such masts require much manual work by the personnel in charge for opening/closing the mast, because the various sections must be opened or closed manually through the use of ropes or suitable bars.
In addition to being difficult to assemble/disassemble, these masts are complex to manufacture and excessively costly due to the large number of constraining members. Also, the mast sections are very delicate because, due to their very complex structure, they very often get stuck while switching from the open configuration to the closed configuration, which may result in damage to the components of the mast structure.
The problem to be solved is, therefore, to articulate the elements of the back of the mast in a manner such that the shoulders can be brought near each other within the specified dimension of 3.3 m, by using a simplified mast structure.
Furthermore, it is desirable to provide a mast which can be easily assembled to the drilling rig, by making the assembly steps simpler and automated.
The present invention aims at overcoming the above-mentioned problems by providing a mast that can be closed to take up less room, and can possibly be divided into a plurality of sections to make transportation easier thanks to the reduced transversal dimension of the mast itself.
Moreover, the operations for assembling the mast sections are carried out with the sections closed, i.e. smaller, thereby facilitating the operations for constraining the various parts thereof.
In particular, the mast structure is simplified, thereby facilitating the construction of the mast components and the operations for opening and closing the mast.